Where do you start to learn to use lathes and mills in
fabrication? Especially if you are interested in using 'em with CNC

One of the best sources is a local community college. Check to see
if they have a Metal Working Technology for similar) dept. Another
source of info is the library. If your library doesn’t have books on
the subject, try lindsaybks.com . Lindsay Books publishes older out
of print books for metal working. Some of the books were written a
looong time ago, but the principals of how lathes & mills work are
still the same. The only differences are improvements in materials &
techniques.

When you get into CNC, there are courses available from software &
equipment mfgrs & GIA & others.